Variable assignment incorrectly pruned within catch clause

[SquidDev]

• Rollup Version: 2.33.1
• Operating System (or Browser): Browser
• Node Version (if applicable): 12.3.1
• Link to reproduction (IMPORTANT, read below): Repl link

First, a disclaimer: I didn't actually write code this horrendous. This is produced by a compiler, hence the rather ... non-conventional JS code.

The REPL example above should be relatively clear. It appears Rollup's optimiser/DCE pass is incorrectly removing a variable assignment within a catch clause.

Expected Behavior

The variable assignment would not be removed. One would expect the above program to print Oh no.

Actual Behavior

The variable assignment is removed, and so result is never assigned. The program prints undefined.

[lukastaegert]

Thanks for spotting this, this was indeed a tricky and interesting one. Fix at #3871.

[SquidDev]

Thank you for the speedy fix ❤️. I know how hard optimiser bugs can be to debug :).